Aerial inventory antenna

ABSTRACT

The present invention relates to a dual polarization radio frequency identification antennae for automatically reading and locating inventory when moved and rotated by an inventory-scanning UAV or robot having three dimensions of position mobility.

RELATED APPLICATIONS

The present application is a continuation-in-part application ofco-pending U.S. patent application Ser. No. 15/286,560 filed 6 Oct. 2016and of co-pending U.S. patent application Ser. No. 14/311,215 filed 20Jun. 2014 that claim priority and benefit based on co-pending U.S.patent application Ser. No. 13/693,026 filed on 3 Dec. 2012 by the sameinventor Clarke W. McAllister. The present application also claimspriority and benefit under 35 USC Section 119(e) of U.S. ProvisionalApplication No. 62,238,105 filed on 6 Oct. 2015 all by the same inventorClarke W. McAllister, the disclosures of which are expresslyincorporated herein by reference. Also the following filed 7 May 2014,and 61/567,117 filed 5 Dec. 2011, and 61/677,470 filed 30 Jul. 2012, and61/708,207 filed 1 Oct. 2012, and of 61/709,771 filed 4 Oct. 2012, allby the same inventor Clarke W. McAllister.

BACKGROUND

The present invention relates to an automated inventory scanning system,including methods and devices utilizing novel aerial scanning antennae,robots, unmanned aerial vehicles, and RFID (radio-frequencyidentification) transponders.

Robots are disclosed for aerial scanning using either propellers to liftan unmanned aerial vehicle (UAV), or a scissor lift mounted to atwo-wheeled robot for maneuvering an RFID antenna to vertical storagespaces that are located well above floor level.

Radio-frequency identification (RFID) transponders enable improvedidentification and tracking of objects by encoding data electronicallyin a compact tag or label. Radio-frequency identification (RFID)transponders, typically thin transceivers that include an integratedcircuit chip having radio frequency circuits, control logic, memory andan antenna structure mounted on a supporting substrate, enable vastamounts of information to be encoded and stored and have uniqueidentification.

RFID transponders rank into two primary categories: active (or batteryassist) RFID transponders and passive RFID transponders. Active RFIDtransponders include an integrated power source capable ofself-generating signals, which may be used by other, remote readingdevices to interpret the data associated with the transponder. Activetransponders include batteries and, historically, are consideredconsiderably more expensive than passive RFID transponders. Passive RFIDtransponders backscatter incident RF energy to remote devices such asinterrogators.

Reflections from shelving and other metal objects in the field of anRFID reader are can blind and possibly saturate baseband amplifierspreventing tag reading. Circularly polarized antennae have nulls thatresult in little or no ability to read linearly polarized RFIDtransponders at certain distance intervals from the antenna. Aerial RFIDscanning also introduces significant ground-bounce problems that alsoresult in poor RFID transponder interrogation performance. These andother problems are overcome by the presently disclosed invention. Noprior art comprehensively teaches systems, methods or devices for movingamong, overcoming carrier reflections, nulls, and ground bounce toautomatically determine the location of RFID-tagged inventory.

SUMMARY OF THE INVENTION

In the present invention seven important problems are solved to makeRFID inventory counting and localization a commercial reality for retailstores engaging in omnichannel retailing, including and especially forretailers that want to use their retail sales for as a forward warehousefor fulfillment of consumer's online orders for same day delivery orin-store pickup. In these highly competitive retail environments such asthis, inventory errors can result in disastrous customer relationshipproblems when a retailer promises delivery or pickup of an item that isnot actually in stock, ready to hand over to a waiting customer.Therefore it is in this context that the following eight solutioncriteria make sense from a retail business perspective: push-buttoninventory, safety, high availability, quiet operation, minimaldisturbance to sales floor, centimeter location accuracy, and lowcapital expense.

Several prior art solutions, including those taught by the presentinventor have not offered solutions that perform as well against theseeight criteria as well as the present invention.

Push-button inventory solutions are achieved when RFID tags are readautomatically. This usually means that some sort of RFID tag scanning isused. RF beams are either fixed or moving. Moving beams are eithermechanically or electronically steered to various locations and vectorangles. The present invention uses an electro-mechanical beampositioning system to steer RF interrogation beam(s), preferably toilluminate and interrogate each RFID tag without incurring direct laborto do so. Robotic solutions are used and optimal robotic mobility isused through aerial RFID scanning.

Safe movement of a robot requires separation of people and object fromfast-moving parts of the robot, including the robot itself. In thepresent invention the requirements for overcoming the force of gravityto lift an move the mass required to form a beam, transmit RF energy,and collect RFID tag data is best achieved by employing lift from ascissor lift apparatus. In the present invention a modified Quadixantenna provides beam focusing from a high gain antenna that weighs onlyabout 3-5 ounces.

High availability is realized by the present invention by a two-wheeledrobot that rolls through tagged inventory items and elevates a rotatingscanning antenna to various altitudes of interest.

In retail sales environments a two-wheeled robot operates very quietly,having no loud moving parts.

Propeller wash is a blast of air that interferes with the shoppingprocess by distracting shoppers and displacing retail inventory anddisplays. The present invention achieves this important designrequirement by eliminating propellers. In the present invention the RFIDscanning antenna is lifted to various altitudes by an expandingmechanical apparatus.

Centimeter accuracy enables high-resolution item localization accuracy.

Low capital expense relative to large arrays of fixed RFID readers isobvious, such solutions do not scale nearly as well as the presentinvention. That is because a single robot can read RFID tags over a muchgreater area than even the best long-range RFID readers. RF beam-steeredRFID readers also have a high cost of the equipment and the wiring thatis required to power them.

The present invention discloses devices for automatically reading andlocating RFID-tagged assets including retail goods, automobiles, andcommercial transport trailers.

Herein the term ‘robot’ is used interchangeably throughout thisspecification and the associated claims to mean either a rolling robotor a flying robot, such as a UAV, except where a specific meaning isexplicitly stated.

Robots of the present invention are optimized and disclosed and claimedfor reading RFID tags in retail store environments where metal displayracks and shelves reduce the read rate and inventory accuracy of systemsthat fail to avoid blinding reflections from typical indoor propagationenvironments. The present invention overcomes limitations of prior artby avoiding unwanted carrier signal reflection paths by using novelscanning devices, features, and methods.

DRAWINGS

FIG. 1 is a directional dual-elliptical UHF RFID antenna according toone embodiment of the present invention.

FIG. 2 is a directional UHF RFID antenna with pitch and yaw axisdirectional mobility according to one embodiment of the presentinvention.

FIG. 3 is a beam pattern of the vertically polarized antenna structure.

FIG. 4 is a beam pattern of the horizontally polarized antennastructure.

FIG. 5 is an RF model of a directional dual-elliptical UHF RFID antennaaccording to one embodiment of the present invention.

FIG. 6 is an RF model of a directional dual-elliptical UHF RFID antennahaving a linear horizontal beam-forming element according to oneembodiment of the present invention.

FIG. 7 is a two-wheeled robot with a scissor lift for aerial positioningof a directional UHF RFID antenna according to one embodiment of thepresent invention.

FIG. 8 is an unmanned aerial vehicle (UAV) with an aerial RFID antennaaccording to one embodiment of the present invention.

FIG. 9 is a directional dual polarization UHF RFID antenna with end-fedexciters according to one embodiment of the present invention.

FIG. 10 is a directional dual polarization UHF RFID antenna with end-fedexciters according to one embodiment of the present invention.

DESCRIPTION OF THE INVENTION

Making reference to various figures of the drawings, possibleembodiments of the present invention are described and those skilled inthe art will understand that alternative configurations and combinationsof components may be substituted without subtracting from the invention.Also, in some figures certain components are omitted to more clearlyillustrate the invention, similar features share common referencenumbers.

To clarify certain aspects of the present invention, certain embodimentsare described in a possible environment—as identification means forretail items that are bought and used by consumers. In these instances,certain methods make reference to items such as clothing, garments,shoes, consumables, electronics, and tires, but other items may be usedby these methods. Certain embodiments of the present invention aredirected for identifying objects using RFID transponders in supplychains, retail stores, warehouses, and distribution centers—both indoorsand outdoors.

Some terms are used interchangeably as a convenience and, accordingly,are not intended as a limitation. For example, transponder is a term forwireless sensors that is often used interchangeably with the term tagsand the term inlay, which is used interchangeably with inlet. Thisdocument generally uses the term tag or RF tag to refer to passive inlaytransponders, which do not include a battery, but include an antennastructure coupled to an RFID chip to form an inlay which is generallythin and flat and substantially co-planar and may be constructed on topof a layer of foam standoff, a dielectric material, or a foldedsubstrate. One common type of passive inlay transponder further includesa pressure-sensitive adhesive backing positioned opposite an inlaycarrier layer. Chipless RFID transponders are manufactured usingpolymers instead of silicon for cost reduction. Graphene tags offersimilar benefits. Inlays are frequently embedded in hang tags, pocketflashers, product packaging, and smart labels. A third type: abattery-assist tag is a hybrid RFID transponder that uses a battery topower the RFID chip and a backscatter return link to the interrogator.

The systems, methods, and devices of the present invention utilize anRFID transponder or wireless sensors as a component. Certain RFIDtransponders and wireless sensors operate at Low Frequencies (LF), HighFrequencies (HF), Ultra High Frequencies (UHF), and microwavefrequencies. HF is the band of the electromagnetic spectrum that iscentered around 13.56 MHz. UHF for RFID applications spans globally fromabout 860 MHz to 960 MHz. Transponders and tags responsive to thesefrequency bands generally have some form of antenna. For LF or HF thereis typically an inductive loop. For UHF there is often an inductiveelement and one or more dipoles or a microstrip patch or othermicrostrip elements in their antenna structure. Such RFID transpondersand wireless sensors utilize any range of possible modulation schemesincluding: amplitude modulation, amplitude shift keying (ASK),double-sideband ASK, phase-shift keying, phase-reversal ASK,frequency-shift keying (FSK), phase jitter modulation, time-divisionmultiplexing (TDM), or Ultra Wide Band (UWB) method of transmittingradio pulses across a very wide spectrum of frequencies spanning severalgigahertz of bandwidth. Modulation techniques may also include the useof Orthogonal Frequency Division Multiplexing (OFDM) to derive superiordata encoding and data recovery from low power radio signals. OFDM andUWB provide a robust radio link in RF noisy or multi-path environmentsand improved performance through and around RF absorbing or reflectingmaterials compared to narrowband, spread spectrum, or frequency-hoppingradio systems. Wireless sensors are reused according to certain methodsdisclosed herein. UWB wireless sensors may be combined with narrowband,spread spectrum, or frequency-hopping inlays or wireless sensors.

A common cause for RFID tags to not read is for a tag to be located at anull in the carrier field. Nulls typically occur at several points alonga beam path between the interrogation antenna and the RFID transponder.Circularly polarized antenna exhibit the problem of vector rotationwherein the propagating electric field from the antenna rotates along aspiral path. If the electric field vector aligns with the transponder'sstrongest polarization, then the tag will readily read. On the contrary,if the field vectors are misaligned, the tags will not read with highprobability.

An operational solution to this problem is to scan again from adifferent angle, polarization angle, and or distance for reducinglocation errors.

Referring to FIG. 1, a preferred beam forming solution is to use dualelliptical antenna 10. It is a high gain circularly polarizedfour-element Quadix antenna, which is an improved antenna that isderived from a much larger, and heavier prior art 146 MHz Ham radiodesign by Ross Anderson W1HBQ. Antenna 10 has advantages such as minimalweight and minimal wind load due to its small surface area. Wind loadforce is calculated as one-half of the density of air times the velocitysquared times the surface area presented to the wind. Antenna 10 has areduced surface area, which when computed over the entire structure onall sides is about 150 square inches.

Preferred embodiments of antenna 10 uses 16 AWG half-hard brass wire forthe elements. The total weight is about five ounces, and when weighed ingrams in any case is less than 200 grams. With respect to a UAV, theseare advantages over a high gain patch or panel antennae, a Yagi-Uda, ora conventional helix with the large reflector that it requires.

This novel antenna, designed for aerial RFID scanning is also related toa bifilar helical antenna wherein its traditional metal ground planereflector that is typically used in prior art helical antennae, isreplaced by the combination of toroidal reflector loop 11 and one ormore director toroidal loops 13. FIG. 5 shows an RF model for thatembodiment. In another preferred embodiment a director is formed by asecond toroid-shaped loop having a smaller diameter than the reflectorloop. In another preferred embodiment, the second director is linearre-radiating element 61, which is a linear horizontal beam-formingelement as shown in the RF model of FIG. 6.

Referring now to FIGS. 3 and 4 the radio frequency beam patterns areshown. FIG. 3 shows beam pattern 31 for the vertical antenna, and FIG. 4shows beam pattern 41 for the horizontal antenna.

Additional directors may be added to further enhance the beam forming.In a preferred embodiment, two, three, four or more linear metallicdirector elements are used to reduce the ellipticity of the verticaland/or horizontal polarized wave fronts, thus resulting in more linearwave fronts. Linear wave fronts have the advantage of consistentalignment of tag and antenna polarizations, regardless of distance alongthe beam path.

The two exciters are fed by two different ports of an RFID interrogatorsuch as the ThingMagic M6e-Micro. In a preferred embodiment, antennaport 1 is connected through coax cable 14 a to balun board 15 a ofvertical exciter 12 a, and antenna port 2 is connected through coaxcable 14 b to balun board 15 b of horizontal exciter 12 b. The balun isa bi-directional electrical device that converts radio frequency signalsfrom balanced to an unbalanced signal. Preferred embodiments also use animpedance-matching circuit on the unbalanced side of the balun to matchthe impedance of the balun to a 50 ohm impedance: 50+j0 ohms. Preferredbalun boards use a 4:1 balun, which would for example have a 200 ohmimpedance on the balanced side and a 50 ohm impedance on the unbalancedside. The balun boards would also preferably have a matching networksuch as a PI network using capacitors and inductors to precisely matchthe impedances, including a 50 ohm impedance for the coaxial cable thatconnects the exciter to one port of the RFID interrogator. The preferredresult is a low return loss of lower than −20 dB at selected frequencieswithin the 860-960 MHz range. In a preferred embodiment, the return lossfor each antenna is less than −10 dB across the 902-928 MHz band, and areturn loss of −25 dB at 915 Mhz. Also preferably, the horizontal andvertical polarizations preferably at any distance are within 2 dB ofeach other. In a dual-linear or dual elliptical antenna, the dominantpolarizations are compared, specifically the vertical polarization ofthe vertical antenna compared to the horizontal polarization of thehorizontal antenna.

The reflector and exciters have a nominal diameters of 4.6 inches andthe director has a nominal diameter of 3.8 inches. The exciter helicalspacing is nominally 1.2 inches. Antenna elements, including theexciters, reflector, director(s), and balun boards are retained in placeby a structure, preferably comprising plastic, such as acetyl copolymer,also known by the popular trade name Delrin. The plastic structure ispreferably attached a to UAV using a mount such as a GoPro mount throughan adapter that engages with mounting slot pair 17.

Referring now to FIGS. 9 and 10 is antenna 90, a preferred embodiment ofa cross-polarized dual-elliptical antenna. Antenna 90 is comprised oftoroidal reflector loop 11 having a diameter of about 4.4 inches whichis retained by plastic reflector support 93, a first helical exciterelement 12 a having a diameter of about 4.0 inches with about 1.2 inchesbetween the turns located on above of the reflector loop, a secondexciter element 12 b having a diameter of about 4.0 inches with about1.2 inches between the turns located above and rotated ninety degrees tothe first helical exciter element, and a toroidal director loop 13having a diameter of about 3.7 inches which is retained by plasticdirector support 94 located above the second helical element 12 b. Thelocation relationships described above are for an upward-pointingantenna 90 with the resulting beam pattern pointing upward above theantenna. In preferred embodiments the reflector, the two exciters, andthe director elements are made of 16 AWG half-hard brass wire; whenmechanically deformed, they return to their originally-manufacturedshape in antenna 90. The toroidal reflector and directors are preferablyformed and then held in a closed loop by soldering or brazing the endstogether.

Unlike a Quadix antenna or antenna 10, antenna 90 has helical exciterelements that are end-fed wherein an impedance matching network,preferably comprising a series-connected fixed inductor and a shuntcapacitor, both connected to the 150 to 200 ohm proximal end of thehelical exciter elements. The two impedance-matching networks arepreferably tuned for the best performance from 900 to 930 MHz; they aremade using printed circuit boards 92 a and 92 b for each wherein the 50ohm unbalanced signal from an active radio circuit is connected througha coaxial cable that is terminated by a coaxial connector, the outershield of which is preferably terminated to a local metal ground. Thelocal metal grounds from both of the impedance-matching circuits arepreferably connected to each other through a conductive metallic skinsuch as copper foil that is wrapped around a hollow central core 91 of astructural material such as plastic. Therefore antenna 90 has a hollowcentral core with its proximal end located about 0.8 Inches above thereflector toroid and a having a polygon shape with about a 1.5 inchcross section and a length of about 2 inches wherein the outer skin isconductive and provides a ground plane for the exciters and a Faradaycage for any circuits that are inside of it to reduce RF coupling ofthem with the electromagnetic fields moving in and around the antennaelements. The resulting relative orientation of the twoimpedance-matching circuits is 90 degrees to each other, like the90-degree relationship between the two exciters. Within the hollowcavity of the supporting structure of the central core, there is spaceprovided for radio circuits. In a preferred embodiment, an RFIDinterrogator such as the ThingMagic M6e-Micro is embedded within thehollow core with a USB cable to provide power and communicationsextending out from it. The two U.FL RF connectors located at each of itstwo RF ports are connected to the RF connectors on each of the twoimpedance-matching circuits that feed the proximal ends of each of thetwo 90-degree oriented helical exciters. In a preferred embodiment, theRFID interrogator antenna interface circuitry alternates between port 1and port 2 to drive an encoded carrier wave through antenna 90 toproduce an electric field with a certain polarization. Then the RFIDinterrogator antenna interface circuitry then drives the other port toemit a second encoded carrier wave through antenna 90 to produce anelectric field with a polarization that is about 90 degrees from thefirst wave. As the RFID interrogator stops modulating the outgoingcarrier wave and listens to incoming backscatter from remote RFIDtransponders, it demodulates and decodes the RF signals that return fromremote RFID transponders.

Unlike antenna 10, preferred embodiments of antenna 90 do not havebaluns for connecting the unbalanced signal from the RFID interrogatorto the somewhat more balance exciter elements. By not having a balunantenna 90 does not have insertion loss or return loss that arecharacteristic of a microwave balun; it also means though that returnsignal currents flow through the coax shield back to the active RFcircuit resulting in the coax cable interfering with the formation ofthe desired radio beam pattern and preferred s-parameters at the feedpoints. Therefore the coax cables are preferably less than 2 inches longand located completely with the conductive skin of the hollow core ofantenna 90 so that the coax cables do not significantly affect the radiobeam pattern or s-parameters.

The first and second helical exciters are formed such that the proximalend of the exciter curls inward to connect with its antenna feed pointas shown in FIGS. 9 and 10. The shape of the curl is preferably that ofa spline that is tangent to the helical part and perpendicular to theplane of the feed point to which its proximal end terminates, the shapeis preferably monotonic.

The conductive skin is preferably made of copper foil and is a goodconductor of both electric current and heat. The radio gain stage, suchas that in the M6e-Micro produces heat, especially at power levels above27 dBm. The heat is preferably conducted to the outer skin of the hollowcentral core. Preferred embodiments use copper ground plane, via arrays,and conductive planes for efficient thermal transfer.

Helical supports 95 a and 95 b are preferably made of plastic and haveminimal contact with exciters 12 a and 12 b, and preferably only at lowvoltage points in the E-fields that circulate through the exciters asshown in FIGS. 9 and 10. ANSYS HFSS antenna modeling software willdisplay E-field vectors that are preferably used to determine thelocations of these points on the antenna elements. The plastic materialsfor helical supports 95 a and 95 b can for example be comprised of ABS,Acrylic, Delrin, Nylon, CPE, or other resins; each different materialhas characteristic dielectric properties such as dielectric constant anddielectric loss tangent that affect the s-parameters of antenna 90 andthe resulting beam pattern. In another embodiment of antenna 90, thecoax cables are longer, extending out from the hollow central core,through the center of the reflector loop, and out the back of theantenna. The conductive skin preferably has a shield connected to itthat does not carry return signal back to an active external radiocircuit.

Antenna 90 preferably has a return loss of about −17 dB, a gain of about8 dB, and a front-to-back ratio of about 20 dB. Antenna 90 whiledelivering these performance benchmarks and operating with dualorthogonal electric field propagation results in an RFID reader antennawith no nulls. This is a significant improvement over prior art RFIDantennae. Since modern RFID transponders that are used for identifyingassets such as as retail items or their containers use simple, low costantenna structures having a single linear polarization, they must beinterrogated by an RFID interrogator and antenna that produce anelectric field that has an E-field polarization that is aligned wellenough to couple energy into and receive backscatter modulation from theRFID transponders.

Prior art RFID antenna that are currently in popular use produce acircular or elliptical field having an electric field (i.e. E-field)vector that rotates through 360 degrees every few feet along itspropagation path to and from remote RFID transponders (i.e. tag). As theE-field vector rotates, there are typically places where an RFID tag isilluminated by an E-field that is oriented about 90 degrees to thelinear polarization axis of the RFID tag. In such cases, the RFID tageither receives insufficient energy to power up, or insufficient carrierwave to backscatter to the RFID antenna and its interrogator. In suchcases, that RFID tag cannot be interrogated at that distance. However asthe distance between the RFID interrogator antenna and the RFID tagchange to either a greater or lesser distance, the energy received bythe RFID tag is sufficient to power up and backscatter data to the RFIDinterrogator. This situation that is described above is commonlyreferred to a null or dead zone. Antenna 90 does not have such nulls ordead zones because there are two polarizations that are concurrentlyavailable for reading RFID transponders; meaning that there is a muchhigher probability that nulls, if observed will typically be observableonly at greater distances between the RFID reader and the remote RFIDtags. This is a significant improvement over prior art.

Antenna 90 is preferably mounted to a robot or a UAV using plasticstructural mount 96. Other preferred embodiments have a second toroidaldirector located above the first toroidal director for increased gain.

Referring now to FIG. 8 unmanned aerial vehicle (UAV) 80 of provides X,Y, Z, rho, theta, phi freedom of aerial mobility. There are several UAVplatforms including quadracopters, tri-copters, hexacopters,octocopters, and helicopters, that are adapted to carrying a directionalUHF RFID reader 81 and antenna 10 for interrogation of RFIDtransponders.

Aerial robot 80 is preferably fabricated from molded plastic andmachined aluminum fittings for the UAV frame and housing of theautopilot and RFID reader 81. Motors turn propellers (shown as a blur asif in rotation) to provide lift, propulsion and to control pitch, roll,and yaw. Commercially available quadcopters such as the Sky-Hero andmulticopters from Align represent aerial platforms that are suitable forconstructing aerial robot 80.

Aerial robot 80 is capable of movement in any direction and in preferredembodiments implements a scan pattern comprising vertical movementsbetween vantage points.

The autopilot preferably contains a 3-axis accelerometer, gyroscope,digital compass, barometer, and CPU. Preferred Pixhawk PX4 embodimentsuse an ST Micro LSM303D MEMS accelerometer/magnetometer. The Pixhawk PX4autopilot from Pixhawk.org is representative of this type of autopilot.It uses a 168 MHz/252 MIPS Cortex-M4F ARMv7E-M CPU with a floating-pointunit. The PX4 also has 14 pulse width modulation (PWM) outputs toservo-control motors and control surfaces, including quad electronicspeed control (ESC). In addition to serving navigation and control loopinputs, the accelerometer is preferably used to report the Z-axisangular attitude of aerial robot 80 and through a known offset angle,the vertical angular component of antenna 10 relative to the earth'sgravitational field. The attitude of aerial robot 80 is preferablyreported to a data collector, preferably using either a serial port(either synchronous or asynchronous) or a universal serial bus (USB).

The data collector is preferably at least comprised of a 32-bit CPU and512M bytes of RAM that are preferably combined into a single module suchas the Broadcom BCM2835 700 MHz ARM1176JZFS. A clock is used to timeRFID data acquired from the RFID interrogator and aerial robot 80attitude reports.

The CPU of the data collector preferably receives an asynchronous streamof RFID tag data from the RFID interrogator that in a preferredembodiment is a ThingMagic M6e-Micro, capable of sending data at a rateof up to 750 tag records per second. Tag read records preferably includeMeta data such as RSSI and are preferably recorded in memory, includingduplicate tag identification numbers. This is unlike prior art RFID tagreaders such as handheld RFID tag readers in that prior art typicallyuse a hash table or similar means to deduplicate tag sightings so thatonly a single tag sighting is reported, sometimes also with a count ofthe number of times that it was seen by the reader. In the presentinvention the CPU uses a time clock to timestamp tag sightings beforethey are stored in memory. In a preferred embodiment, the CPU and memoryare combined within a single device such as the Broadcom BCM2835.

Memory preferably holds records of each tag read and their correspondingtimestamp. Estimated flight position and attitude of aerial robot 80 arealso recorded with timestamps. Preferred embodiments also run a flightpattern of rows along various headings in order to enhance RFID taglocation data sets recorded in memory. Each point where RFID scan datais collected is a vantage point.

Vantage point computations preferably consider the downward angle ofantenna 10 relative to the top plane of aerial robot 80 as shown in FIG.8. Except when hovering in one place, aerial robot 80 also has angularoffsets in pitch, roll, and yaw that must be considered. The gain andresulting beam shape of antenna 10 also determines the amount of angularuncertainty for each RFID tag reading.

A vital characteristic of the directional antenna is that it be bothvery light and have a minimal surface area in order to reduce wind load.Wind load is particularly important with respect to air rushing past theUAV's propellers and applying wind load pressure on the antenna, whichincreases the load on the UAV. Wind load is also a risk when operatingthe UAV scanner outdoors or in an area with large fans for aircirculation, such as large industrial warehouses. Weight is always aconcern for aircraft design; the antenna is a payload for the UAVaircraft to carry. Therefore, less weight is better. The presentinvention discloses an antenna that uniquely meets these vitalcharacteristics.

GPS signals are preferably used for guiding robots while readinginventory such as cars in outdoor automobile lots.

There are many indoor locations where GPS signal strengths are too lowfor indoor GPS guidance. This section teaches solutions to that problemby using location references within the volume that is scanned forRFID-tagged inventory items. Unlike GPS, the scan volume may be indoorsand/or outdoors.

The instant invention discloses location references that send or receivesonar pulses or send/receive laser light in order to provide locationand heading information for robots.

The location references have locations within a constellation map thatis communicated to the robot. In a preferred embodiment, the threedimensional location of each location reference are compiled to create aconstellation map. The constellation map is preferably communicated toeach robot via Wi-Fi. In a preferred embodiment, the constellation mapof location references is transmitted using either TCP or UDP packets.Using UDP packet, the constellation maps are broadcast such that eachmobile device in the vicinity can use an internal dictionary or databaseto lookup the location of each location reference by its designatornumber.

Preferred embodiments of robot 70 or UAV 80 use one or more VL53L0Xlaser ranging modules from ST. Each has a 940 nm VCSEL emitter (VerticalCavity Surface-Emitting Laser) for a Time-of-Flight laser rangingmodule. It measures the distance to objects that reflect light, atranges of up to 2 meters. Preferred embodiments use these small sensorsto sense people and objects in the environment around robot 70 or UAV80. They offer a key advantage for retail store scanning applicationsbecause the VL53LOX will sense fabric items such as saleable retailstore apparel that would not be detectable by sonar sensors.

In other preferred embodiments sonar or ultrasonic ranging is used tomeasure time-of-flight of sound bursts referred to as pings. When asound transmitter and a receiver are in the same place it is monostaticoperation. When the transmitter and receiver are separated it isbistatic operation. When more transmitters (or more receivers) arespatially separated, it is called multistatic operation. The presentinvention uses all three types, each wherein a sonar transmitter createsa pulse of sound called a “ping”, and the sonar receivers listen for theping. This pulse of sound is created using outputs from electroniccircuits. A beamformer is used to concentrate the acoustic power into abeam.

In the present invention, to measure the distance from robot 70 to anode, the time from transmission of a ping to a reception node ismeasured and converted into a range by knowing the speed of sound. Tomeasure the bearing or attitude, estimates are made using the rotationof robot 70 and from the directional beams from each of the sonartransmitter transducers.

The location of robot 70 is accurately determined using at least four ofthe sonar receiving nodes that listen for sonar pings from robot 70ultrasonic transmitter array. The locations of each of the receptionnodes is first determined using surveying tools including laser rangefinders, tape measures, or ultra wideband time-of-flight localizationsystems. In a preferred embodiment radio transmitters are based on chipssuch as the Maxim MAX7044 which is a 300 MHz to 450 MHz High-efficiencycrystal-based+13 dBm amplitude shift keying (ASK) transmitter having a250 us oscillator start-up time and 40 nA standby current. The sonarreceiving nodes are preferably powered by a long-life battery such as a3-volt lithium coin cell and all components have very low (i.e.micro-amp level) leakage current and CMOS circuitry, including op-ampTLV2764 with 20 uA per channel supply current and a unity gain of 500KHz. Sonar receiving nodes preferably remain powered on with theirultrasonic receivers actively waiting for acoustic waves from robot 70,at which time the MAX7044 powers up, its oscillator starts, and the CMOScircuitry serially transmits a selectable identifier to the MAX7044 formodulated data transmission. For a 303 MHz carrier, and while using a9.84375 MHz crystal, the CLKOUT clock signal is 615.2 KHz, which whendivided by 8 provides a 76,900 bits per second data rate.

Other preferred embodiments use Bluetooth Low Energy (BLE) nodes insteadof the narrowband radio chips described above. Use of these requires atime-synchronization technique for accurate measurement oftime-of-flight readings.

The sensor network is used to for trilateration computations. Note thatthe time-of-flight between radio waves and acoustic waves differ by sixorders of magnitude due to the differences in the speed of light(300,000,000 meters per second) and the speed of sound (344 meters persecond). The time-of-flight of the radio waves are well below thesensing threshold of the electronics used in the present invention.Since acoustic energy dissipates over distance according to the squarelaw, the amplitude of the reflected ping wave front is reduced by thedistance to the fourth power.

Navigation through an RFID-tagged facility requires that the positionand attitude of robot 70 be known. Preferred aerial scanning systemsinclude reference points and signaling methods that relate to theposition and attitude of robot 70 relative to those reference points.Types of references and signaling methods use radio waves and oracoustic waves. Types of radio waves include GPS signals, Wi-Fi signals,narrowband, spread spectrum, and ultra wideband (UWB) signals. Preferredembodiments also use micro-machined 3-axis 3D accelerometers,gyroscopes, and barometer, and magnetometers to sense acceleration,angular velocity, and heading and feeding those sensor measurements intocomputer 16 where control loops and estimator algorithms run. In apreferred embodiment computer 16 is an ODROID-XU4 from Hardkernel Co.Ltd. Of South Korea, having Samsung Exynos5422 Cortex™-A15 2 Ghz andCortex™-A7 Octa core CPUs. Preferred embodiments include sensors such asST Micro LSM303D 14-bit accelerometer and magnetometer, ST Micro STMicro L3GD20H 16-bit gyroscope, Invensense MPU 6000 3-axisaccelerometer/gyroscope, and MEAS MS5611 barometer.

Preferred control loops and estimator algorithms are available andadapted for use with robot 70 from open source autopilot developercommunities such as PX4 and Paparazzi. Both are open-source autopilotsystems oriented toward inexpensive autonomous aircraft. PX4 flightstack module source code is available athttps://github.com/PX4/Firmware/tree/master/src/modules.

Another preferred embodiment uses a Qualcomm Technologies FlightPlatform based on Linux operating system, a Qualcomm Snapdragon 801processor and 4K Ultra HD video, computer vision, navigation, andreal-time flight assistance. Project Dronecode is porting PX4 to operatein multi-threaded embodiments that will run on symmetric multiprocessing(SMP) Qualcomm Hexagon under a Linux operating system.

In a preferred UWB embodiment a DecaWave ScenSor DWM1000 Module is usedfor an indoor positioning system. DWM1000 is an IEEE802.15.4-2011 UWBcompliant wireless transceiver module based on DecaWave's DW1000 IC.DWM1000 enables the location of objects in real time location systems(RTLS) to a precision of 10 cm indoors.

In a preferred embodiment a combination of narrowband or spread spectrumradio signals within an appropriate frequency band and acoustic waves astaught herein where a radio signal is used to indicated time of arrivalof an acoustic ping at a remote sensing location. Time-of-flight ofacoustic waves is used to compute distances with raw accuracy on theorder of 1 centimeter.

Range measurements from fixed reference points are preferably used intrilateration computations to determine robot 70 position and attitude.A preferred trilateration calculation method uses four points where onepoint will be the origin (0, 0, 0), one point will lie on the x-axis (p,0, 0), and one will lie on the xy-plane (q, r, 0). The fourth point willhave an arbitrary location (s, t, u). This results in the followingequations for x, y, and z where “Sq(p)” for example means p to the powerof 2 and SqRt( ) is the square root operation:

x=(Sq(d1)−Sq(d2)+Sq(p))/2p

y=(Sq(d1)−Sq(d3)+Sq(r)+Sq(q)−(q(Sq(d1)−Sq(d2)+Sq(p))/p)/2r

z=+/−SqRt((Sq(d1)−Sq((Sq(d1)−Sq(d2)+Sq(p))/2p))−Sq((Sq(d1)−Sq(d3)+Sq(r)+Sq(q)−(q(Sq(d1)−Sq(d2)+Sq(p))/q)/2r))

Using a nominal conversion factor of 147 us per inch, the distancecovered by a wave front traveling at the speed of sound is 50 ms/147 us,which equals 340 inches or 28.34 feet.

Other preferred embodiments of the present invention include cameras forphotography, retail store surveillance, and for reading barcodes.Barcode decoding algorithms including open source algorithms. In apreferred embodiment a Samsung 5Mpixel K5ECG MIPI CSI sensor is used forcapturing still images or videos.

In a preferred embodiment, robot 70 have an API for shoppers to takecontrol of BIS 10 or 80 for amusement and for shoppers taking photos ofthemselves and their friends inside or outside of the retail store (i.e.“selfies”). In that embodiment retail stores benefit from attractingcustomers and making it fun for shoppers to use this in conjunction withsocial media to show their friends the clothes, footwear, or handbagthat they are interested in at that retail store, thus attractingadditional business from the shoppers' friends.

In a preferred embodiment LIDAR sensors, such as LIDAR-Lite fromPulsedLight, Inc. of Bend, Oreg. (now owned by Garmin International) areused for determining the range to surrounding objects, people, orfixtures. Precise angle measurement can also be obtained whilemonitoring outputs from the Lidar-Lite 3 as Laser Rangefinder it isrotated around an axis, observing reported ranges. As the laser spotpasses over a section of reflective tape with corner cube reflectorsembedded in it, a range discontinuity is reported; this is because thecorner cube surface reflects nearly all of the photons from the Lidarback to the Lidar, into the its optical light receiver, overwhelming itwith excessive signal. Preferred arrangements of Lidar-Lite rotationangles and placement of sections of reflective tape provide a enablemeasurement of both distance and angle of the environment surroundingit.

In other preferred embodiments RADAR is used to scan the areasurrounding BIS 10 using GHz range scanning technology that is adaptedfor UAV use from companies that include Silicon Radar GmbH of Frankfurt,Germany. The 122 GHz FMCW frontend contains a 122 GHz SiGe transceiverchip fabricated in IHP SG13S SiGe BiCMOS technology, transmit andreceive antenna (LCP substrate)—bonded in a standard pre-mold opencavity QFN package covered by a special lid. The IC is an integratedtransceiver circuit for the 122 GHz ISM-band with antennas. It includesa low-noise-amplifier (LNA), quadrature mixers, poly-phase filter,Voltage Controlled Oscillator with digital band switching, divide by 32circuit and power detector.

Preferred embodiments include simultaneous localization and mapping(SLAM) functions for constructing or updating a map of an unknownenvironment while simultaneously keeping track of the location of robot70 within the map. Preferred embodiments use a particle filter or anextended Kalman filter.

In a preferred embodiment, use a Lidar that emits laser light,preferably in the 600 to 1000 nm wavelength range. A laser diode isfocused through a lens apparatus and directed usingmicroelectromechanical systems (MEMS) mirrors for example. Preferredlaser beam scan patterns include general forward-looking patterns,sweeping the area in front of the UAV, or patterns that sweep throughbroader angles including a full 360-degree field of view. Raster scanpatterns sweep through yaw and azimuth angles. A Lidar receives andanalyzes the reflections off of objects that surround robot 70. Returnlight is amplified and processed to create a map or to determine theposition of robot 70 within an existing map for navigation.

In preferred embodiments for retail stores having overhead lighting,including fluorescent or incandescent lighting emit sufficient energy inthe form of light, electrostatic fields, or heat that can be harvestedto power an optical location reference.

Solar cells such as monolithic photovoltaic strings CPC1824 ormonocrystalline KXOB22_01X8F, both manufactured by IXYS, are examples ofpreferred solar cells that convert photons from indoor fluorescentlighting into electric current. These energy harvesting devices powerpreferred embodiments of location references the present invention.

Using a shaft encoder, robot 70 measures the angle of the direction inwhich it is transmitting a laser beam from laser 24 of FIG. 2 relativeto the body of the robot. Laser 24 rotates as antenna housing 25 rotatesthrough yaw angles, scanning the area around it.

In a preferred embodiment, robot 70 rotates a laser line from a laser 24such as a 980 nm 60 mW laser line module from Lilly Electronics. Theline is oriented in a vertical direction such that it is swept by therotation of housing 25 of FIG. 2 around in a circle that surrounds robot70. The controller of robot 70, such as an Intel Compute Stick noteswhen the laser line passes a reference point and at what angularvelocity. Surrounding detectors having a pair of photodiodes such as BPW34 FASR from OSRAM with an integrated daylight optical filter and thatare especially sensitive to wavelengths of light in the range of 730 to1100 nm. When the 980 nm laser strikes and briefly illuminates the firstphotodiode, the signal is amplified by a transimpedance amplifier usinga low power op amp. The photodiodes are preferably fed into a differenceamplifier so that common mode noise will cancel. Optical noise fromsunlight and fluorescent lighting is therefore subtracted and eliminatedfrom the output signal to a processor such as a Bluetooth Low Energy(BLE) module. In a preferred embodiment a Microchip BM70 is used to timethe pulse arrival times and report them to robot 70 over a Bluetoothlink. A timer in the BM70 processor measures the time of arrival of thepulse. Then too when the laser strikes the second photodiode, which isin a preferred embodiment located only 2 inches to the side of the firstphotodiode, the time of that pulse is also measured and recorded. Bycomparing the times of the strikes to the reference time and angularvelocity that are known by robot 70, the angles are computed for thelaser path from robot 70 to each of the two photodiodes. From those twoangles and the triangles formed by them along with forward and lateralreference lines, the location of robot 70 is estimated. Accuracy isdependent on the accuracy of each measurement. Preferred embodiments useseveral such BLE/photodiode modules to report laser strike observationssuch that robot 70 combines the aggregate of the location estimates toimprove the accuracy of the fused triangulation estimate.

Triangulation computations for computing the location of a transponderuses a base line reference. The location of the transponder is computedusing the law of sines. Then using the known locations of robot 70 alongwith its various antenna positions is preferably converted into astore-level coordinate system such as Cartesian coordinates with anx,y,z ordered triplet of axes to record the location of transponders. Ifthe tag is a location transponder that marks location coordinates, thenthe location of robot 70 is back-calculated and updated. Robot 70preferably uses accelerometers, gyros, and shaft encoders on wheels 71 aand 71 b to sense motion, acceleration, posture, and dead reckoningmovement to estimate the position of robot 70 between location tagreadings and location references.

Cameras are also preferably used with tracking the centroid of opticalreferences, optical flow, and vanishing point navigation to recognizeand guide a path for robots through aisles. Optical flow is the patternof apparent motion of objects, surfaces, and edges in a retail storecaused by the motion of the camera. Vanishing point navigation uses theparallel lines of store aisle, shelves, windows, and overhead lightingrails to compute a distant target, such as the end of an aisle; it alsoprovides visual angular alignment for squaring the robot for accuratetriangulations and transponder location measurements.

Beams and optical patterns of various types are dispersed through thesurrounding space in order to provide an optical point of reference. Insome embodiments dispersion is achieved using motion, moving mirrors,and/or other optical elements. In other embodiments, dispersion isachieved using fixed optical elements.

Two-wheeled robot 70 uses a variable pitch RFID scanning antenna such asscan head 20 to direct an RFID interrogation field to selected vectors.Pitch axis 22 a and 22 b are supported by antenna support structure 21.Push rod 23 is preferably driven by a wing servo, causing antenna 10 topivot to various controlled pitch angles. A small gear motor thatrotates housing 25 controls the yaw angles for antenna 10 and laser 24for triangulation measurements in support of robot localization.

Scan head 20 has a battery or super capacitor to store energy that isused to drive the RFID interrogator, a data collector, a pitch axismotor, and a yaw axis motor. Preferred embodiments of the data collectoruse an Intel Edison that provides an ARM processor, a small form factorwith Bluetooth, Wi-Fi, and adequate memory to store RFID records.

Scissor lift members 74 are preferably strong, light, and able toconduct electric current to scan head 20 for recharging the battery orsuper capacitor. Preferred embodiments of scissor lift members 74 usematerials such as carbon fiber rods or long thin printed circuit (PC)boards made from FR4 fiberglass. PC boards with dimensions ofapproximately 0.25″×21.5″ preferably use conductive traces to conductcharging current to scan head 20. Members 74 each have three pivot holeswith metal plating; one hole at each end of each PC board and one holein the middle to form the scissor lift structure. Preferred embodimentsuse wires such as half-hard 16 AWG brass wire soldered between the PCboards to form intersecting triangles for structural strength.

Four lift bars 73 are preferably driven by two gear motors that rotatefrom a nominally horizontal angle to an elevated angle of approximately70 degrees. Scissor lift members 74 are attached through pivots to liftbars 73 and expand vertically and collapse in response to movement ofthe lift bar motors. Significant heights of scan head 20 are realized byadding more lift members 74.

The RFID reads from various vantage points and selected vectors as anaggregate prevent missing any transponders from among a plurality oftransponders that prior art readers would miss by either lack ofillumination or blinding reflections from the interrogation field.Preferred embodiments use narrow RF interrogation beams, formed by highgain antennae that greatly reduce the magnitude of reflections fromoff-axis signal vectors that prior art solutions typically receive andprocess from a plurality of responsive transponders, resulting inambiguity of the transponders' actual locations; an ambiguity thatgreatly confounds tag location efforts.

Robot 70 reads the identity and actual locations of RFID-taggedmerchandise. Robot 70 as shown in FIG. 7 determines the locations oftagged goods in retail stores. In this preferred embodiment, there aretwo wheels 71 a and 71 b that independently rotate in either a clockwiseor counter-clockwise direction to create forward or reverse motions ofrobot 70 or in opposing directions for a route turn or rotation of robot70 about a fixed point on the floor.

Battery 72 c is mounted below axles of wheels 71 a and 71 b to provide alow center of gravity; the result is inherent stability, unlike that ofa classic inverted pendulum robot or a Segway human transporter.

As robot 70 traverses a retail sales floor or inventory storage areas,it may from time to time encounter obstacles in an otherwise flatsurface. Robot 70 is preferably comprised of accelerometers and athree-axis gyroscope that detects changes in position and angularorientation. A robot controller such as a tablet, iPad, ODROID XU4, orIntel Compute Stick preferably detects and responds to changes inorientation under the control of algorithms that take into account theduration of the disturbance and historically related information.Controller 70 preferably learns by recording previous encounters withobstacles at certain locations, and reuses successful maneuvers toescape from known obstacles.

Robot 70 is preferably comprised of proximity sensors such as sonarmodules to detect obstacles and boundaries. Sonar modules preferablyreport range to objects that reflect acoustic waves and enable robot 70to stop or to take evasive action. Escape maneuvers of robot 70preferably include reversing, pivoting, and changing direction to goaround obstacles such as walls, furniture, and movable objects.

The controller preferably communicates with an RFID reader locatedwithin housing 25 using a wired or wireless connection. Information fromthe RFID reader is preferably collected and stored. In a preferredembodiment, SGTINs are associated with location information. In someembodiments, location is information is augmented by reading fixedlocation RFID transponders that are encoded with location codes.

Transponder location information preferably references a system orreferences points that extend beyond the boundaries of the room or spacein which robot 70 is operating. A plurality of transponders cantherefore have a distance between them that is greater than the physicaldimensions of the space that they are contained within. For example, ina preferred embodiment, RFID location transponders are encoded withhigh-resolution longitude and latitude information. A preferred locationidentifier for an RFID transponder uses GPS coordinates. Such a locationsystem is preferably used to track the locations of goods on a globalscale.

A database preferably collects transponder identities and locations fromrobot 70 and others like it in facilities around the world. The robotsperiodically upload data to the database as Wi-Fi, 3G, or 4G wirelessservices are available.

The database preferably comprises means to report the locations ofassociated transponders to consumer devices wherein the associations aredefined by characteristics of the objects that the transponders areattached to. The associations preferably comprise characteristics thatinclude and are defined by fashion, style, or personal preferences. Thedatabase preferably accounts for fashion and style changes and altersthe associations so that consumers will be more likely result to buy.

In this and other embodiments the narrow beam improves transponderlocation accuracy by reducing off-axis reads and reflections thatconfound tag location efforts. When an aggregate number of such readsare processed using triangulation, then the resulting tag locationaccuracy is greatly improved over prior art systems, methods, anddevices.

In preferred embodiments motors for wheels 71 a and 71 b are polyphasebrushless DC (BLDC) motors such as three-phase BLDC motors with Halleffect sensors or back EMF sensing to sense the angular velocity andposition of the rotor. Exemplary motors are 100 to 500 watt hub motormeasuring about 5 to 9 inches in diameter that benefit from massproduction for e-bikes that have become globally popular, wherebydriving costs down. Preferred embodiments of robot 70 use motors thathave sufficient torque and traction to climb ramps and stairs in orderto successfully scan all parts of multi-level environments. Due to thelack of brushes, BLDC motors will not spark, making them better suitedfor use in environments where there are volatile chemicals or fuels.

Micro-stepping of BLDC motors using sine-cosine phasing is used inpreferred embodiments. Micro-stepping motor drives preferably include atorque feedback loop that controls the current through an H-bridge oneach phase using phase current modulation such as pulse width modulation(PWM) to switch phase current on and off in a controlled manner,allowing freewheel current to circulate through a freewheeling diode foreach phase as the magnetic flux gradually subsides in a current waveformthat resembles a saw tooth. Preferred embodiments use coreless motorswith Litz wire coil windings to reduce eddy current losses and wheelweight. Current and therefore torque delivered to motors is preferablycontrolled by a proportional-integral-derivative (PID) control loop.

Wheels 71 a and 71 b preferably have spokes to a rim for holding a tiresuch as a Bell Solid Tube NoMorFlat tire for bicycles. The spokespreferably provide an axle height above the floor that enablessufficient clearance for counterbalancing mass and weight to be placedbelow the axle whereby moving the center of gravity for the entire robot70 below the axles. In preferred robot embodiments batteries 72 a-ccomprise a significant part of that counterbalancing mass and weight.Lead acid, LiNiMnCo, LiFePO4, lithium phosphate, or lithium-ionbatteries deliver 20-50 amps to wheel motors in preferred embodiments ofbatteries 72 a-c.

Preferred embodiments of robot 70 include self-aligning rechargeconnections for parking robot 70 in a location where it can guide itselfto recharge batteries 72 a-c. In preferred embodiments, batteries 72 aand 72 b are moved fore or aft to shift the center of gravity of robot70, maintain balance and an upright position.

In preferred embodiments, high gain antenna 20 rotates to generatemultiple beam path vectors that result in multiple read occurrences fortriangulation computations to reliably determine the location of eachdetected transponder. Preferred embodiments use a shaft encoder tomeasure the angle of antenna housing 25 relative to a body of robot 70.

Referring to robot 70 of FIG. 7, antenna 10 is free to rotate about itsyaw axis to provide the item level inventory count and location accuracythat is demanded by retailers and needed for multi-channel shopping. Theantenna must be swept in a methodical and controlled manner fortriangulation computation as described above.

The above calculations are based on the use of narrow beam, high gain,directional antenna 10 directed along selected vectors in order for thetriangulation computations to be valid and accurate. In preferredembodiments, the antenna gain has a minimum of 8 dBic in order to form anarrow interrogation field from an RFID interrogator coupled with theantenna, for reading tags in a narrow sector of RFID-tagged inventoryitems at any one time. This narrowly focused beam reduces theprobability that a scan will be blinded by un-modulated carrier beingreflected into the receiver or for off-axis transponders to confoundlocation by being illuminated and responsive to the carrier beam.Preferred embodiments detect amplifier saturation from blindingreflections and record the beam vector and location of blinding carrierreflections. Avoidance of or saving points of location reference arepreferred uses of that stored information, enabling multi-dimensionalalignment of scans from day to day.

Inventory rounds are preferably swept across the tag from multipleangles, preferably using a high gain antenna in order to reduce themagnitude of location error.

Intermediate transponder location data preferably comprises transponderobservations that are used for triangulation computations. Scan resultsare preferably reported in stages, the second stage comprising: SGTIN;observation point (i.e. location of robot x,y,z); viewing angle(elevation and azimuth); and RF power level (db). Each stage is storedand processed to produce a computation of each tag's location using adescriptor comprising: SGTIN; and computed X, Y, Z Cartesian location.The processing comprises the steps of:

-   -   1) Match all first stage SGTIN observations and consolidate the        detection records    -   2) Match any second stage observations to the consolidated first        stage records    -   3) Combine the first and second stage records by formulating the        three dimensional vector for both stages and compute the        Cartesian point of intersection.    -   4) Match the result to any previous result of computed X, Y, Z        location in a third stage. If there are no matches, then store        as final stage transponder location data.

While the invention has been particularly shown and described withreference to certain embodiments, it will be understood by those skilledin the art that various changes in form and detail may be made withoutdeparting from the spirit and scope of the invention.

I claim: 1) A dual polarization antenna for scanning RFID transponderscomprising: a hollow central core having a polygon shape with about a1.5 inch cross section and a length of about 2 inches wherein the outerskin is electrically conductive; an RFID interrogator wherein theinterrogator is located within the hollow central core with two antennafeed points on the surface of the skin; a toroidal reflector loop havinga diameter of about 4.4 inches; a first helical exciter element having adiameter of about 4.0 inches with about 1.2 inches between the turns andlocated above the reflector loop wherein the proximal end of the excitercurls inward to connect with a first one of the antenna feed points; asecond helical exciter element having a diameter of about 4.0 incheswith about 1.2 inches between the turns and located above the firsthelical exciter element wherein the proximal end of the exciter curlsinward to connect with a second one of the antenna feed points; atoroidal director loop having a diameter of about 3.7 inches wherein thedirector loop is located above the second helical exciter element. 2)The antenna of claim 1 further comprising a second toroidal directorlocated above the first toroidal director. 3) The antenna of claim 1,wherein the reflector, exciters, and director elements are made of 16AWG brass wire. 4) The antenna of claim 1, wherein the reflector,exciters, and director elements are made of half hard brass wire. 5) Theantenna of claim 1, wherein the proximal ends of the exciters are fed byan impedance-matching network. 6) The antenna of claim 1, wherein theexciters are mechanically supported at low voltage points. 7) Theantenna of claim 1, wherein the outer skin is thermally conductive